Electron gun for heating materials in an evacuated container

ABSTRACT

An electron gun for heating materials in vacuo, including an electron beam source, an electron lens, a deflector, yoke means connecting the deflector and winding means.

' [451 Mar. 28, 1972 8 m M M c H mm m w e R m N .U m U D ME T mm m V E F N A UN GMR WLE um T ET E M W L EMC 4 H Walter A. Dietrich, Hanau am Main;

313/84 ....313/84 3/1970 Takemoto et 13/84 2,840,740 6/1958 Bickford.................................. 3,247,411 4/1966 2f BlL Ww 3,504,211

Verwaltung [72] inventors:

l-lelmut G. M. V. Dellery, Grossauheim e M212. b

FORElGN PATENTS OR APPLICATIONS 1,248,175 8/1967 Germany...................,...........219/121 GmbH,

[73] Assignee: Leybold-Heraeus C ologne-Bayental, Germany [22] Filed: Feb. 25, 1970 Primary Examiner-J. V. Truhe Assistant Examiner-Gale R. Peterson Attorney-Joseph F. Padlon [21] Appl. No.:

[30] Foreign Application Priority Data Nov. 6, 1967 7] ABSTRACT An electron gun for heating materials in vacuo, includin electron beam source, an electron lens, a deflector, means connecting the deflector and winding means.

Germany......................P 19 55 846.4

gan yoke [52] U.S. Cl............,.........219/l2l EB, 250/495 TE, 313/84 Int. [58] Field oiSearch.................313/84; 250/495 TE, 49.5 D;

219/121 EB 2 Claims, 3 Drawing Figures PATENTED m 2 8 I972 lnyntar:

SHEET 1 BF 2 A ii PATENTEBMAR28 I972 3.652.821

' sum 2 HF 2 MMfl Attorney.

ELECTRON GUN FOR HEATING MATERIALS IN AN EVACUATED CONTAINER The invention relates to an electron gun for heating materials inan evacuated container. Said gun consists of a source of abeam of electrons, at least one electron lens, and at least one deflector unit arranged substantially symmetrically relative to the beam for deflecting the beam in the interior of the container, a vacuum-tight beam guiding tube being interposed between the axis of the beam on the one hand and the electron lens, the winding and the yoke of the deflector unit on the other hand, the tube being adapted to be connected with the container, and the free end of the tube being closed by the source of the electron beam.

An electron gun of the aforedescribed type is known, for example, from published German Pat. application No. 1,248,175. The known gun, when in the assembled condition, has an electron lens and a deflector unit which project into the interior of a container capable of being evacuated in which a heating process is to be performed. Materials of all kinds may be molten, welded or evaporated thereby. The portion of the gun extending into the container is equipped with a cooling jacket for protecting the heat sensitive coils of the electron lens and of the deflector unit. The known gun, however, is only of limited applicability to containers in which an extremely high vacuum is to be generated and to be maintained during the operation of the gun. However, an extremely high vacuum is needed particularly for many coating processes by vacuum evaporation. As is well known, the internal face of the vacuum container must be degassed thermally if the required low pressure is to be achieved, that is, the container walls must be brought to a temperature high enough so that the residual gas molecules are released from the wall portions and can thereafter be pumped off. The necessary temperatures frequently are in the range up to 400 C. and sometimes even higher. However, the known guns are not suitable for such high temperatures for the following reasons: When water cooled, the surfaces of the gun projecting into the container cannot be thermally degassed. In the absence of water cooling, the electrical insulation of the magnet coils would be destroyed. It is not permissible to remove the gun, because the vacuum in the container would be destroyed.

With the above in view, it is an object of this invention to provide a gun of the aforedescribed general type which permits thermal degassing of the wall portions directed toward the interior of the vacuum container without endangering the heat sensitive structural elements thereof. Moreover, the electron gun assembled with the container is to be kept quickly ready for operation regardless of the thermal degassing procedure.

These above objects are achieved by releasably mounting the winding and the yoke of the deflector unit as well as the electron lens on the beam guiding tube in such a manner that they may be withdrawn without releasing the vacuum in the container. A particular problem which had to be solved in arriving at this solution resided in the fact that the electron beam is to be deflected in the interior of the container so that the portion of the deflector unit which actually causes the deflection of the beam must be located within the container. This necessary condition heretofore prevented thermal degassing of the vacuum container and of the gun connected thereto.

In order to permit the deflector coil to be removed in a particularly simple manner, it is proposed according to the instant invention that the pole pieces and the yoke with the winding of the deflector unit constitute separate sub-assemblies, the pole pieces being adapted to be fixedly connected with the vacuum container, and the yoke with the winding being adapted to be slipped from the beam guiding tube. Such an arrangement satisfies all requirements listed above and is additionally distinguished by its simple and reliable construction over the art.

A preferred embodiment of the invention will not be described with reference to the appended drawing in which:

FIG. 1 is a vertical sectional view of an electron gun of the invention attached to a partly illustrated vacuum container in elevational section;

FIG. 2 shows the embodiment of FIG. 1 in an elevational, partly exploded view on a smaller scale; and

FIG. 3 is a perspective exploded view of the deflector unit of the apparatus of FIG. 1.

Referring initially to FIG. 1, there is seen an electron gun 1 whose principal elements are a source 20f an electron beam, an electron lens 3, and a deflector unit 4 fordeflecting the electron beam 5 in the interior of a container 6 at an angle from its original axis.

The electron source consists essentially of a thermal emission cathode 7 partly shielded by an apertured cap 8 or Wehnelt cylinder and an acceleratoranode 18 which is at ground potential, a high potential being established between the electrodes during operation of the gun. The electrodes are connected to a nonillustrated high-voltage line by two plugs 9,10 cooperating with contacts (not shown) in a socket 1 1 of insulating material mounted on a flange 12 on a tubular, ceramic, high-voltage insulator 13 in vacuum-sealing relationship. The plugs 9,10 also supply filament current for the cathode 7.

The end of the insulator 13 remote from theflange 12 carries another flange 14. A counter flange 15 is connected to the flange 14 by nonillustrated bolts and nuts, and the two flanges 14,15 are sealed to each other by interposed spacer rings 16,17 which envelop the accelerator anode 18 having the shape of a hollow conefFlange 15 is connected to a beam guiding tube 19 which provides a vacuum-tight connection between the electron source 2 and the vacuum container 6.

The end of the tube 19 remote from the source 2 is provided with a radial flange 20 of nonferrous metal sealed to a cooperating flange 22 on the container 6 by means of an O- ring 21, of asbestos or soft copper.

As is also shown in FIGS. 2 and 3, deflector unit 4 includes an approximately U-shaped magnet core of iron consisting of two leg portions 23 carrying respective pole pieces 24 and a yoke 25. The two leg portions 23 and the yoke 25 are three separate structural units whose faces 26 are abuttingly engaged in the assembled condition of the gun for transmitting magnetic flux. The leg portions 23 are fixedly fastened to the flange 20 in vacuum-tight engagement. The yoke 25 is a flat ring whose principal plane is perpendicular to the axis of the straight tube 19. Diametrically opposite parts of the yoke carry integral axial abutment lugs 27 of the same cross section as the respective, abuttingly engaged leg portions 23, and each carrying a coil 28 of the magnet winding. When the coils 28 are energized through nonillustrated conventional leads, a magnetic field is generated between the pole pieces 24 having lines of flux approximately perpendicular to the axis of the electron beam and therefore deflecting the latter, the magnitude of the deflection being a function of the exciting current under otherwise identical conditions.

The yoke 25, the coils 28 and the electron lens are mounted in a shell 29 of generally cylindrical shape, as shown. A spacer non-ferromagnetic ring 38 such as insulating material separates the lens 3 from the deflector unit 4 to avoid interference with the magnetic fields. The shell 29 and the elements mounted thereon may be slipped from the tube 19 in an axially upward direction, as viewed in the drawing. This normally rests on a collar 30 on the tube 19. The radial bottom wall of the shell 29 is apertured for passage of the tube 19 and of the leg portions 23.

Electron lens 3 is equipped with an iron sleeve 32 with an opening of the same dimensions as the central opening 37 of yoke 25 to permit the shell 29 with the attached devices to be slipped over the electron beam source 2. l

The top end of the shell 29 is covered with an annular plate 33 which supports a protective cap 34 for electron source 2. It is provided with an external, grounded, metallic coating too thin to be shown in FIG. 1. The central opening 35 of plate 33 is wide enough for passage of the electron source 2 therethrough. Plate 33 is normally connected with the counter flange by a nonillustrated bayonet closure which holds the shell 29 axially against the collar 30 when engaged. The central portion of plate 33 is axially enlarged for coaxially securing the top end of the shell 29.

When shell 29 and the elements mounted thereon are lifted from tube 19 and the electron source 2 as shown in FIG. 2, and the plugs 9,10 are released, the remaining, heat-resisting structure may safely be heated as needed for degassing the walls facing the evacuated space while container 6 is connected to a high-vacuum pump in a conventional manner, not shown.

Deflector unit 4 shown in the drawing permits beam 5 to be deflected in one plane only. It will be appreciated that the illustrated apparatus may be equipped with a second analogous unit offset 90 from the unit 4 so that beam 5 may scan all portions of a plane in the container 6 which is horizontal in the view ofFlG. 1.

What is claimed is:

1. In an electron gun for heating materials in an evacuated container comprising, in combination, a source of a beam of electrons, an electron lens, a deflector unit having two leg portions carrying respective pole pieces, yoke means for connecting said leg portions, winding means adapted to be energized for inducing magnetic flux in said leg portions, in said yoke means, and between said pole pieces while said beam passes between said pole pieces, a vacuum-tight, beam guiding tube separating the axis of said beam from said electron lens, said yoke means, and said winding means, one end of said tube being sealed and carrying said source, and sealing means on the other end of the tube for sealing said tube to said container in communication with the interior of the same, mounting means releasably mounting said winding means, said yoke means and said electron lens on said tube for removal from the same without breaking a vacuum in said tube when the tube is sealed to said container by said sealing means, and the container is evacuated, said vacuum-tight electron beam guiding tube being releasable, said source of electrons for said tube being fixed inside one end thereof, said electron lens being outside the tube, said tube extending into the vacuum container, said yoke means surrounding said tube exterior of said vacuum container, said winding means being on said yoke, said deflector having an approximately U-shaped magnetic core with two legs, each leg having a portion exterior of said vacuum container and another portion projecting into said vacuum container, a pole piece for each of said legs interior of said vacuum container in opposed relation to each other for deflecting said beam, said yoke means including an annular yoke member having a central opening dimensioned for movably receiving said tube, and abutment portions projecting from diametrically opposite parts of said yoke member and carrying said winding means and adapted to releasably connect said leg portion exterior of said vacuum container.

2. In a gun as set forth in claim 1, wherein said leg portions have respective free abutment faces, fastening means for fixedly fastening said leg portions to said container, said yoke means including two abutment portions, said abutment portions respectively engaging said abutment faces for passage of magnetic flux therebetween when said yoke means are mounted on said tube by said mounting means, and said tube is sealed to said container by said sealing means. 

1. In an electron gun for heating materials in an evacuated container comprising, in combination, a source of a beam of electrons, an electron lens, a deflector unit having two leg portions carrying respective pole pieces, yoke means for connecting said leg portions, winding means adapted to be energized for inducing magnetic flux in said leg portions, in said yoke means, and between said pole pieces while said beam passes between said pole pieces, a vacuum-tight, beam guiding tube separating the axis of said beam from said electron lens, said yoke means, and said winding means, one end of said tube being sealed and carrying said source, and sealing means on the other end of the tube for sealing said tube to said container in communication with the interior of the same, mounting means releasably mounting said winding means, said yoke means and said electron lens on said tube for removal from the same without breaking a vacuum in said tube when the tube is sealed to said container by said sealing means, and the container is evacuated, said vacuum-tight electron beam guiding tube being releasable, said source of electrons for said tube being fixed inside one end thereof, said electron lens being outside the tube, said tube extending into the vacuum container, said yoke means surrounding said tube exterior of said vacuum container, said winding means being on said yoke, said deflector having an approximately Ushaped magnetic core with two legs, each leg having a portion exterior of said vacuum container and another portion projecting into said vacuum container, a pole piece for each of said legs interior of said vacuum container in opposed relation to each other for deflecting said beam, said yoke means including an annular yoke member having a central opening dimensioned for movably receiving said tube, and abutment portions projecting from diametrically oppoSite parts of said yoke member and carrying said winding means and adapted to releasably connect said leg portion exterior of said vacuum container.
 2. In a gun as set forth in claim 1, wherein said leg portions have respective free abutment faces, fastening means for fixedly fastening said leg portions to said container, said yoke means including two abutment portions, said abutment portions respectively engaging said abutment faces for passage of magnetic flux therebetween when said yoke means are mounted on said tube by said mounting means, and said tube is sealed to said container by said sealing means. 